1. Field of the Invention
The invention relates to a photosensitive resin composition; particularly, to a white photosensitive resin composition for producing a white matrix, and for further producing a color filter and reflective display element.
2. Description of the Related Art
Nowadays, in the development of a flat panel display (FPD), a liquid crystal display is the most widely used for it's thinning and miniaturization. However, watching the liquid crystal display with backlight source for long periods of time usually brings eye fatigue and causes injury to users. The optical characters of liquid crystal display frequently change with the change of viewing angle.
To improve the above-mentioned problems, a reflective display device has been developed. The reflective display device can be more thinner, reduce more power and lighten the burden on user's eye.
The reflective display is a display which uses the incoming ambient light to reflect to display the image, such as a reflective liquid crystal display device and an electronic paper display device, etc.
The electronic paper display device is a new technology, it can transform the words on paper. The above-mentioned “paper” is made up of organic electronic materials actually and it use microspheres which are affected by electric field to display. The pixel transform of the electronic paper display is similar with the person computer, and it refreshs the pages by pixel transform.
The materials of the microsphere of the electronic paper display device include conductive plastics. The pigment of Gyricon Bead was first developed in the 1970s by Xerox. Gyricon Bead is electrostatic microspheres with a black side and a white side. The electrostatic microspheres rotate when the electric fields changed and then could have black, white, gray scale and bring out the display of documents.
In the 1990s, another type of the electronic paper display was invented by Joseph Jacobson at the Massachusetts Institute of Technology (MIT), it used microcapsules instead of the traditional electrostatic microspheres. The microcapsules are filled with color oil and white charged particles. The white particles move up (close to user) or move down (far away from user) via the control of the external electric field. When the white particles move up, it display white and when the white particles move down, it display the color of oil. This type of the electronic paper display device is the application of electrophoresis techniques and the display device could be used to the flexible plastic substrate instead of glass by means of microcapsules.
The color electronic paper display has two ways to display in color: one is using RGB/CYM instead of the white particles and the other is putting a color filter on the electronic paper display device.
A color filter can be produced directly on the glass substrate in a hard electronic paper display device, but the cost is high. To assemble the glass substrate and the color filter in the electronic paper display device is more difficulty. On the other hand, the color filter cannot be produced by the above-mentioned method in a flexible electronic paper display.
Another low-cost method is forming the pattern of the color filter on the display layer of the electronic paper display device. The color filter is made up of photosensitive resins as mentioned in Japanese Patent Publication No. 2009-531727. The pattern of the color filter is formed with a photosensitive resin composition, and the material of the shading part is a black resin composition. However, as to the reflective display using ambient light to display pattern, light transmittance and light utilization efficiency are down and bad brightness.
To improve the above-mentioned problems, Japanese Patent Publication No. 2008-129599 disclose using a white photosensitive resin composition as the shading part. Although this could improve the light utilization efficiency but it has the shortcoming such as poor heat-yellowing resistance, surface roughness resistance, developability and brightness.
Therefore, it still needs to develop a white photosensitive resin composition with good heat-yellowing resistance, surface roughness resistance, developability and brightness to enhance the development of electronic paper display device.